I am here to help you out, @care-lizzom-com.

Let's access your QuickBooks account using a private browser or an incognito browser. This way, we can isolate if this is browser-related. 

First, make sure you're logged in as the Master or Company Admin. Adding an additional user or an accountant in your account requires admin rights. 

Next, the stored history on your regular browser may have been corrupted thus preventing you from adding your user. Let's switch to a different browser and try it one more time. You may use either of these browsers:

• Chrome: Ctrl+Shift+N
• Firefox: Ctrl+Shift+P
• Safari: Command+Shift+N

Also, you can clear the cache or delete temporary internet files from your regular browser. That'll remove previously-stored browsing data that might have caused the issue. Here's a complete guide on how to do that: How Do I Clear My Browser Cache And Temporary Internet Files?

In the meantime, please follow the workaround listed below:

1. Log in to your QBO account.
2. Click the Gear icon at the right top.
3. Under Your Company, select Manage Users.
4. On your browser, change the URL to app/legacyusermgt.
   
5. You'll be directed to the old page where you can add an accountant.
   

Once done adding a user, don't forget to toggle the URL to app/usermgt. This will route you back to the new page.

If you're still unable to add an additional user, it's possible that you're using QuickBooks Online Simple Start version. We can add up to two accountants in Simple Start, Essentials, and Plus plans. You can browse this article for more insights: How many users can I set up?.

Leave a reply below if you have other questions about managing your authorized users in QuickBooks. I'm always here to help.